High polymer materials used as biomaterials are required to have functions suitable for their applications, such as non-exothermicity, non-toxicity including non-allergenicity, mechanical strength for adapting to tissues and living organisms, ability to separate substances, and ability to release drugs in a sustained manner.
For example, anti-adhesion films used for preventing postoperative tissue adhesion are required to have good adaptability, non-adhesiveness, and low irritativeness to tissues, quick bioabsorbability for dispensing with postoperative removal, and excellent mechanical strength and flexibility in a dry state, which affect the handling property of the films.
Conventional biomaterials, however, are not sufficiently balanced in required functionalities or the like, so that development of materials is desired that fulfill the above requirements in a balanced manner.
A-B-A triblock copolymers are conventionally known, wherein segment B is polyethylene glycol, and segments A on both ends of segment B are modified amino acid groups, such as poly-β-benzyl-L-aspartate (abbreviated as PBLA hereinbelow) or poly-γ-benzyl-L-glutamate (abbreviated as PBLG hereinbelow) (WO00/771602). Such polymers have good kinetic properties, but have a relatively slow biodegradation rate. Thus, when embedded in a large amount in the body, the polymers may not disappear completely in a short period of time, though rarely.
On the other hand, as bioabsorbable materials, there are known hyaluronic acid, collagen, carboxymethyl cellulose, polycaprolactone, regenerated cellulose, polylactic acid, polyglycolic acid, and copolymers of these. However, none of these materials may easily be given an ideal bioabsorption rate or have sufficient mechanical strength and flexibility.